The problem of ink drying on nozzles was countered by the A. B. Dick company in U.S. Pat. No. 3,346,864 showing a nozzle cover to be used when the printer is not operating. Ricoh in Japan solved the same problem by introducing in U.S. Pat. No. 4,045,802 an automatically operating cap to seal orifices not in use.
The problem of replenishing ink solvent evaporated from returned ink was addressed by The Mead Corporation in U.S. Pat. No. 3,761,953, by A. B. Dick in U.S. Pat. No. 3,771,568, and by IBM in U.S. Pat. No. 4,130,126. Each used a different method to monitor changing ink characteristics due to solvent depletion. The most general claim, not specifying which sensing means is used, was in the Mead patent.
Evaporation occurs from all exposed ink surfaces including ink mist, satellite drop surfaces, unused drop surfaces, etc. Some of the evaporation problem, especially that associated with mist, is alleviated in the system shown in U.S. Pat. No. 4,023,182 issued to A. B. Dick. It shows a vacuum return from the region of the catcher of unused droplets. it also shows an air-ink separator. However, the air leaving the separator has become saturated with ink solvent vapor and thus represents a loss of solvent from the system.
In other patents, porous droplet catcher components, porous acceleration rings, and even porous deflection ribbons are pumped clean of ink by negative air pressure (vacuum), but in any of these systems the air traveling to the pump becomes nearly saturated with ink solvent. Thus, since air is never shown recirculating to the ink selection region, the pumping represents a loss of solvent, the corresponding pigment being returned to the system.
Recirculation of ink is shown but not claimed in U.S. Pat. No. 3,512,173 by D. E. Damouth. The recirculation had been assumed in prior art patents.
With regard to a second aspect of my invention showing a droplet selection method best suited for operation in very high vapor atmosphere without special guards against condensation, there are several examples in former art of convex surfaces being used to capture and guide droplets to a catcher. One is my own invention shown in U.S. Pat. No. 4,138,686. In U.S. Pat. No. 3,813,675 Mead Corporation shows a conductive ink guiding convex surface with channels therein, and an electric field directed toward said channel containing surface to urge charged droplets thereonto. In U.S. Pat. No. 3,836,914 Mead shows a convex drop guiding surface with changing curvature increasing toward an ingesting blade. An electric field and charged droplets are again mentioned in their claims. A third Mead catcher is shown in U.S. Pat. No. 4,035,811. In this catcher liquid of the droplets is captured by a convex surface and deflected while touching the surface more than ninty degrees from the original droplet path direction. Original droplet paths are claimed as downward and ingestion is claimed as upwardly directed.
The IBM Corporation uses a convex catching surface in U.S. Pat. No. 3,893,623 in a somewhat different way, no voltage being applied to the droplets on or before contacting the surface. They also use gravity implicitly to trap droplet splatter.
The new art of the second aspect shown in my current invention concerns new surface configurations and modes of selective release from a surface. Electrically induced changes in contact angles of droplets on a surface are used, as was the case in my former U.S. Pat. No. 4,138,686, which shows more general claims.
With regard to a third aspect of this invention, much work has been done on surface chemistry and on hydrophobic surfaces. A book titled "Hydrophobic Surfaces", edited by Frederick M. Fowkes, gives some data relevant to this patent. If an ink composed of metal is to be used, then U.S. Pat. No. 3,596,285 assigned to Teletype is relevant. It shows a low melting alloy being deposited on a steel band in the form of visible letters to be read directly. A continuous stream of liquid metal hits the band; whereas, in my invention the metal is controlled in droplet form, and the product may be used as type in a printing press or as a wiring connecting otherwise separate terminals.
Whether metal or water based ink is used, a thin (few thousand Angstrom) dielectric layer capable of withstanding 100 volts is shown in U.S. Pat. No. 3,670,130, assigned to International Standard Electric Company. This dielectric layer and similar layers can form part of the control surface which contacts ink droplets. To this I add the concept of adding an additional low energy surface coating to produce large contact angles for liquids contacting the control surface, or liquids being switched in electrostatic switches.
It is therefore one object of this invention to provide a means to prevent ink from drying on certain surfaces of a printer. It is also an object to prevent significant loss of ink solvent in unused recycled ink, the loss not being compensated for by a similar loss of ink pigment or other ink components. Some droplet selection schemes best adapted to benefit from this prevention means will be discussed.
Another object is to provide particular new aspects of a selection system claimed herein. All droplets touch a convex surface. The surface attracts the ink only weakly, with large contact angle, except when voltages are applied immediately beneath the convex surface. Thus some drops will leave the convex surface either suddenly or gradually and proceed to an output means, while other droplets will be captured by the surface and sent to a collection area. Elements of this new scheme are shown in U.S. Pat. No. 4,138,686 assigned to this applicant, but specific additions to surface design, ink surface interaction, ink used, and printer purpose are made.
Certain hydrophobic surfaces and electrically spark resistant thin layers will be claimed in combination in relation to the above selection scheme.